Known bearings include various means for guiding and positioning rollers. Bearing types include journal bearings wherein a shaft is rotatably supported by an outer ring. Journal bearings typically require a lubricant (e.g., high pressure oil) to be pumped between and around the shaft and an interior surface defined by the outer ring. Needle roller bearings are another type of bearing. Needle roller bearings have a plurality of cylindrical shaped rolling elements, generally referred to as needles, disposed between the shaft and the interior surface defined by the outer ring. Thus the shaft is rotatably supported by the needles. Needle roller bearings require less lubricant than journal bearings. Needle roller bearings also operate at lower friction levels than comparably sized journal bearings. However, needle roller bearings have higher contact pressures on the shaft at the rolling interface with the needles. Thus the operating life of needle roller bearings is generally less than comparably sized journal bearings. Needle roller bearings are easily contaminated by debris such as byproducts of combustion generated in an engine. Such byproducts are abrasive and can cause wear and premature failure of the needle roller bearing.
Roller bearings can be used for reducing friction between components of engines. For example, tappet roller bearings can be incorporated into an engine valve drive mechanism for minimizing friction of the valve drive mechanism components. In general, to reduce friction on an engine and thus reduce fuel consumption, tappet roller bearings are fitted to the mechanism which changes the rotation of a cam shaft synchronized with an engine crank shaft into the reciprocal drive for the intake valve and exhaust valve.
Diesel engines such as those used in higher mileage applications of light, medium and heavy duty vehicles typically use journal type bearings in cam follower applications because of their ability to operate without significant wear for over 250,000 miles to as much as one million miles of operation. However, journal bearings require a pumped supply of high pressure lubricating oil to operate in such applications. There has been a long felt and unfulfilled need for lower friction cam follower bearings for use in such higher mileage applications. However, despite significant efforts, those skilled in the relevant art have been unable to design a needle roller bearing that has a sufficient life suitable for use in diesel engines for such higher mileage applications.